1. Field of the Invention
This invention relates to airless paint sprayers and, more particularly, to the design of tips used in the spray guns of such sprayers.
2. Description of the Prior Art
A typical airless paint sprayer includes a pump, a suction tube having one end coupled to the pump inlet and the free end insertable in a container of paint, and a high-pressure hose that connects the pump outlet to a spray gun. Typically, a check valve is installed at the pump outlet. The spray gun has a trigger which, when depressed, opens a valve to allow pressurized paint in the hose to flow through a nozzle in the gun tip. The paint is atomized as it exits the nozzle, allowing a painter to evenly apply the paint to a surface. Although there are dozens of manufacturers of airless paint spraying equipment, the function of the equipment is basically the same. Differences in the available equipment usually relate to the design and output capacity of the pump. The three most common types of pumps used in airless paint sprayers are diaphragm pumps, piston pumps and gear pumps.
The capacity of pump unit, the high-pressure hose length, and the number of spray guns connected to the pump unit will determine the maximum tip size. A sprayer having an output capacity of xc2xd gallon per minute (gpm) can comfortably support a single spray gun using a tip nozzle in the 0.015 to 0.021-inch (about 0.38 to 0.53 mm) diameter range. Required pump capacity increases by about the square of the nozzle size.
Referring now to FIG. 1, a spray gun 100 used in combination with airless paint spraying systems typically has a hollow, pistol-shaped body 101. The body 100 incorporates a handle 102, a squeezable trigger 103, a trigger guard 104, and an internal valve assembly 105, controlled by the trigger 103, that controls the flow of paint to an output barrel 106. The handle 102 typically doubles as a housing for a removable screen filter (not shown). At the bottom of the handle 102 is a threaded coupling 107, to which the high-pressure hose from the pump unit may be attached. Attached to the end 108 of the output barrel 106 is a spray tip assembly 109.
Referring now to FIGS. 2 through 6, a typical spray tip assembly 109 includes a tip housing 201 having, at a first end thereof, a connector 202 that attaches to the end 108 of the output barrel and, at a second end thereof, a spray guard 203 that reduces the possibility of that a user of the equipment will inject paint into his body through the skin. The tip housing 201 generally incorporates a cylindrical bore 204 that is sized to receive a cylindrical shaft 301, that is generally referred to as a spray tip. At the mouth of the cylindrical bore 204 on one side of the tip housing 201 is a semicircular recess 205. When the spray tip assembly 109 is installed on the spray gun 100, the cylindrical bore 204 is perpendicular to the axis 401 of the gun output barrel 106. The cylindrical shaft 301 is sized for slidable entry into the cylindrical bore 204, with minimal clearance so as to prevent leakage of paint between the cylindrical surface of the shaft 301 and the cylindrical surface of the bore 204. For this particular prior art spray tip assembly 109, the cylindrical shaft 301 is secured within the bore 204 with a semicircular spring clip 501.
Still referring to FIGS. 2 through 6, the shaft 301 incorporates a single nozzle 302, the axis of which is perpendicular to the axis 303 of the shaft 301. At one end thereof, the shaft incorporates a handle 304, which facilitates both removal of the of the shaft 301 from the tip housing 201 and rotation of the shaft 301 to reverse the nozzle 302 should it become clogged. The handle 304 may incorporate a stop 305 which, in combination with the semicircular recess 205, allows the shaft 301 to be rotated only within an arc of 180 degrees. At one end of the arc, the nozzle 302 is positioned for spraying; at the other end of the arc, the nozzle 302 is positioned for unclogging.
Professional painters typically use several interchangeable tips of different sizes and/or different spray patterns at the same job site, the size and pattern of the tip being dictated by the particular application. For example, a tip with a 0.035-inch-diameter nozzle might be used for rapid application of latex base coats, while a tip with a 0.015-inch-diameter nozzle might be used for the painting of trim. In order to change to a different tip, the installed tip must be removed and stored for future use, and the desired tip installed in its place. The need to switch tips affords an opportunity for uninstalled tips to become lost. As the retail cost of each tip is about $US 30, the loss of multiple tips equates to a significant needless expense. There is also an additional economic waste related to the time required to switch out the tips.
U.S. Pat. No. 5,255,848 to Nolin C. Rhodehouse discloses a multiple orifice spray tip having reversible orifice cleaning capability for use with airless paint sprayers. A first embodiment spray tip offers first or second orifice by vertical movement of an orifice selection cylinder, while a second embodiment offers selection of a first or second orifice by rotation of the orifice selection cylinder about a vertical axis. There is a major disadvantage with each of these embodiments. The first embodiment requires an indexing tab to be attached with a screw at the end opposite the handle. This screw and indexing tab are problematic for two reasons. First, a screwdriver or other similar assembly tool is required to remove the spray nozzle. Therefore, the screwdriver must be carried to jobs and stored in a secure location. Secondly, construction sites are seldom neat and without clutter. Thus, if either the screw or the tab is dropped during disassembly or assembly, there is a fair likelihood that it will not be recovered. The disadvantage of the second embodiment is that tip manufacture is complicated by the nonlinear paths which the paint must take for each orifice. The additional complication will inevitably lead to production costs which are greater than for a tip which may be manufactured in a more straightforward manner. In addition, the nonlinear paint paths may affect the evenness or symmetricalness of the spray pattern.
Also available on the market is a product called DoubleShot(copyright), which is a tip having two identically-sized orifices. Installation of a collar on the tip permits the orifice farthest removed from the handle to be used. Once the collar is removed, the orifice nearest the handle may be used. This product, however, does not address the need for multiple orifices of different sizes.
What is needed is a spray gun for airless paint sprayers which permits rapid changeover of spray nozzles without tools and, which does not require removable fasteners or other small parts which are readily misplaced or lost, and which permits both single and multiple orifice spray nozzle to be used with the same spray gun and tip guard.
The present invention provides a new spray tip assembly that may be used in combination with conventional spray guns for airless paint sprayers. The spray tip assembly incorporates a tip having multiple nozzles, each of which may be used independently. Several embodiments of the invention are contemplated.
For a first embodiment of the invention the shaft of the spray tip assembly incorporates multiple spaced apart nozzles and a handle at one end thereof. The shaft also incorporates a spring-loaded detent ball. The tip housing has a bore with a plurality of spaced-apart annular or semi-annular grooves, each of which, in conjunction with the spring-loaded detent ball, serves as a shaft locator for each of the nozzles. The grooves permit positioning of each of the nozzles in either a normal spraying position or in a reversed, unclogging position.
For a second embodiment of the invention, the tip housing incorporates three spaced-apart annular channels, all three of which are interconnected by a slot shaped to admit a stop tab attached to the shaft. More accurately, the outermost channel is really a semicircular recess, shown in the prior art description as item 205, as it is open on one side. The stop tab may be indexed with any one of the channels, thereby serving to position the shaft so that each of the nozzles may be respectively and independently positioned for use.